Conventionally, a microphone using an acoustic sensor, called an ECM (Electret Condenser Microphone), has been used as a small-sized microphone. However, the ECM is weak against heat, and a microphone (MEMS microphone) using an acoustic sensor manufactured by using a MEMS technique is superior in terms of coping with digitalization, of miniaturization, of enhancement of functionality/multi-functionality, and of power saving. Accordingly, in recent years, the MEMS microphone is being often employed.
The acoustic sensor (MEMS sensor) manufactured by using the MEMS technique is an acoustic sensor fabricated by using a semiconductor integrated circuit fabrication technique. The acoustic sensor includes a diaphragm electrode and a back plate electrode that are provided on a semiconductor substrate so as to form a capacitor.
Then, when a sound pressure is applied to this MEMS sensor, a conductive vibrating membrane (diaphragm) vibrates, and the distance between the vibrating membrane and a fixed membrane (back plate) including a fixed electrode changes. This leads to change in capacitance of the capacitor formed by the vibrating membrane and the fixed electrode. The MEMS microphone measures a change in voltage as caused by this change in capacitance, thereby outputting the sound pressure as an electrical signal. Configurations of MEMS sensors are disclosed in Patent Literatures 1 to 3.
Patent Literature 1 describes a microsensor which uses a silicon substrate as a fixed electrode and which has a vibrating membrane provided on the silicon substrate.
Further, as with Patent Literature 1, Patent Literature 2 describes a silicon condenser microphone (sensor) which uses a silicon substrate as a fixed electrode and which has a vibrating membrane provided on the silicon substrate.
Furthermore, Patent Literature 3 describes an acoustic transducer including: a conductive vibrating plate; and a perforated member isolated from the vibrating plate by an air gap and supported by a substrate.